A man understood to have been granted refugee status was deported from a Melbourne detention centre.
Photograph: Dave Hunt/AAP

The immigration department has secretly deported a man to Nauru from a Melbourne detention centre, according to lawyers and advocates.

The man, who is understood to have been granted refugee status, was allegedly removed from the Mita facility on Thursday night without warning and without being able to contact his legal representatives.

It’s believed he was in Australia for medical treatment, but it’s not known if that treatment had ended.

Legal cases have been filed on behalf of those individuals and the government gave a formal undertaking in the proceedings before the high court that there would be three days’ warning given to legal teams of any planned deportation.

“A decent and compassionate government which respects the rule of law doesn’t choose to secretively deport people found to be refugees in the middle of the night without any transparency, due process or access to legal advice,” said Daniel Webb, director of legal advocacy at the Human Rights Law Centre (HRLC).

Webb said the man was not a client of theirs, but did have legal representation.

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The Department of Immigration told Guardian Australia it did not comment on individual transfers.

The HRLC is representing 320 people currently in Australia after being transferred from Nauru for medical care.

Webb said the shock deportation, coupled with the government’s discussion of permanent visa bans on refugees this week, had distressed those on Nauru and Manus Island, and in Australian detention.

“There are kids in our classrooms right now who in the space of the last few days have heard [the prime minister] Malcolm Turnbull threatening lifetime bans and now seen someone in a similar situation to them secretly deported,” he said. “They are understandably afraid and really unsettled. What are they supposed to say to their friends at school? It’s fundamentally cruel.”

The immigration minister, Peter Dutton, has said the new rules are essential to stop people coming into Australia “through the back door” and entering into “sham relationships”. However, he has failed to explain why current screening processes are not adequate.

Labor has ridiculed the proposal and criticised the government for changing its messaging from day to day, but refused to rule out supporting it as it had not been provided with any legislation to assess.

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On Friday morning, the leader of the House, Christopher Pyne, said the legislation would be released “as soon as it’s ready to be introduced, because it’s pretty straightforward”.

The government has maintained it is still in talks with several countries to act as third-party settlement destinations for the refugees processed offshore, but released no details.

There are suggestions the US and Canada may be involved. New Zealand’s prime minister, John Key, said there had been no new discussion with the Australian government and that New Zealand would not support the creation of “different classes of citizens”.